1. Field of the Invention
The present invention relates to a device for deaerating a fiber stock suspension.
2. Description of the Related Art
Devices for the deaeration of fiber stock suspensions are well known to the experts in the industry. As the name indicates, these devices deaerate fiber stock suspensions. During deaeration minor contaminates which would otherwise interfere with paper or cardboard production are removed. The devices are large tanks into which the fiber stock suspension, that is to be supplied to the paper or cardboard machine, is fed in the form of a thin mixture. The functional principle of the device is that the fiber stock suspension is boiled in a vacuum, the gas is removed to a so-called gas chamber, and the other minor impurities present on the liquid surface in the tank are discharged. The fiber stock suspension which is to be supplied to the paper or cardboard machine is removed through an opening in the tank floor, located there for the purpose of removing fiber stock suspension from the tank that is as gas free as possible. In order to maximize the deaerating capabilities of the device, a vacuum is generated in the tank by a pump, whereby the gas is forced through a line from the tank. The deaerating capability is improved when the supplied gas-containing fiber stock suspension is fed into the tank through steel pipes located above the liquid level in the tank, whereby the gas which is present in the added fiber stock suspension, possibly in the form of bubbles is discharged prior to coming into contact with the already present fiber stock suspension. In addition to stabilizing the liquid level, the single overflow is used to remove minor contaminations from the liquid surface in the tank, so they do not reach the paper or cardboard machine. The minor contaminates flow over the single overflow to the discharge and then on to further treatment.
German Disclosure Document DE 42 34 522 A1 describes a deaeration chamber in accordance with the aforementioned generic term of the present invention, as used in the paper and pulp industry. The separation wall which forms the overflow for the separated, excess fiber stock suspension is essentially level with the rear edge of the outlet for the gas-free suspension and the overflow for the separated, excess suspension itself slopes toward the overflow in the tank, in opposite direction to the flow direction.
Further disclosures regarding the position and shape of the separation wall forming the overflow for the separated, excess fiber stock suspension may be found in the German prior art documents DE 32 19 740 A1, in the PCT application WO 97/15717 and in U.S. Pat. No. 5,868,905 (PK10542 US).
All aforementioned documents share the disadvantages with regard to the overflow for the separated, excess fiber stock suspension in that the separation wall is located transversely and symmetrically to the tank axis (longitudinal axis), that it""s location is a given due to it""s shape, meaning that it is located on one of the two end areas of the tank and it""s overflow length is fixed.
The present invention provides a device for deaerating of fiber stock suspension where the overflow for the separated, excess fiber stock suspension can be located independently from both the inlet for the fiber stock suspension and the outlet for the deaerated fiber stock suspension. An overflow in the shape of an overflow pipe having an overflow height and an overflow length located prior to the outlet opening for the separated, excess fiber stock suspension, viewed in the flow direction.
In one embodiment of the invention a dwell chamber in the form of a hydraulic stabilizer is located after the outlet opening for the gas-free fiber stock suspension. The dwell chamber consisting of preferably a long horizontally cylindrical tank, with at least one inlet opening to accept the fiber stock suspension coming from a prior tank. The tank having outlet openings for the separate discharge of the. gas-free fiber stock suspension, the separated gas, the excess fiber stock suspension and the separated, excess fiber stock suspension. The opening for the discharge of the separated excess fiber stock suspension being an overflow tube having an overflow height and an overflow length.
By designing the overflow for the separated, excess fiber stock suspension as an overflow tube having an overflow height and an overflow length, a design advantage as well as a fluidic advantage is achieved in that the overflow for the separated, excess fiber stock suspension may be positioned at any desired location in the tank; rather than being positioned transversely and symmetrically to the tank axis in one of the two end areas of the tank. Further, the design of the overflow length may be freely selected within a certain range.
In one embodiment of the invention the overflow pipe has a funnel shaped opening with an aperture angle of between 30xc2x0 and 80xc2x0, preferably between 40xc2x0 and 50xc2x0. This type of initial opening has an advantage in that the opening orifice area of the overflow tube is independent from the continuing diameter of the overflow tube. In addition, the flow geometry can be positively influenced by the selection of the aperture angle.
One embodiment of the invention provides that the overflow tube be a telescopic structure, thereby offering a changeable overflow height. Changeability of the overflow height provides the option to control the liquid level in the tank, or to regulate it, if a drive unit including a control system are present, whereby the liquid level will influence the dwell duration and the dwell volume of the fiber stock suspension in the tank. The telescopic construction of the overflow tube may be a sliding device.
A further embodiment of the invention provides, that the overflow tube including the discharge pipe be movable, thereby providing for an adjustable overflow height. The discharge pipe of the overflow tube also may have a transition piece whose length and shape are adjustable so that, even if the overflow tube is moved, no local shifting occurs in the subsequent system. The transitional piece would preferably be in the form of folded tubing.
In yet a further embodiment of the invention the overflow tube is a telescopic and divergent structure, providing for an adjustable overflow length. An increased overflow length provides the advantage of additional abatement due to reduced flow in the separated, excess fiber stock suspension.
In a preferred embodiment of the invention, the overflow tube can be coupled with at least one tube segment, thereby providing adjustability for the overflow height and/or the overflow length. Depending upon the shape of the pipe segment, the configuration may influence the overflow height and/or overflow length without having to fall back upon expensive and operationally critical mechanisms.
In a further embodiment of the current invention the outlet opening for the separated, excess fiber stock suspension is located between the inlet opening for the fiber stock suspension and the outlet opening for the gas-free fiber stock suspension. Thereby the contaminated fiber stock suspension can be brought directly, without having to pass the outlet for deaerated fiber stock suspension, to the outlet opening and be removed.
In another embodiment of the invention the tank includes at least two outlet openings for separated, excess fiber stock suspension, whereby at least one outlet opening is designed as an outlet in the form of an outlet pipe with an overflow height and an overflow length and the additional outlet openings are equipped with covers. The presence of multiple outlet openings offers the technological advantage that the overflow which is designed as an overflow pipe may be located at various positions in the tank and therefore, it""s specific location can be selected to best suit the fiber stock suspension characteristics.
In a further embodiment of the invention an overflow, designed as an overflow pipe with an overflow height and an overflow length is located prior to the outlet opening for the gas-free fiber stock suspension, as viewed in the direction of flow. The advantage is that the overflow for the gas-free fiber stock suspension can be placed at any desired location in the tank. It further provides the advantage that different volumes can be discharged in a fluidically optimum manner, by means of different size openings.
In a further embodiment of the invention a device is provided for producing vacuum in the tank including a vacuum connection, a vacuum line and at least one vacuum pump. Several vacuum connections can, at any given time, be operated individually with a separate vacuum line and a separate vacuum pump, or with individual vacuum lines and a common vacuum pump.
A further embodiment of the invention provides that in the upper interior tank area several nozzles are located for moistening the interior surface of the tank which does not come into contact with the fiber stock suspension, whereby the speed and efficiency of the fiber stock deaeration process taking place in the tank is positively influenced. Moisturizing also prevents fiber stock or ash deposits.
It is also advantageous if the distributer pipe is parallel or approximately parallel to the tank axis. The distributer pipe can be outside or inside the tank. This arrangement results in spacial (space requirement) and technological (distribution uniformity) advantages.
In a further embodiment of the invention the hydraulic stabilizer for the preferably gas-free fiber stock suspension is a dwell tank having a certain dwell duration and a certain dwell volume having fluidically optimum interior contours. The fluidically optimum interior contour is that of a horizontal cylinder, or that of a conical tube, aligned in the direction of flow of the fiber stock suspension. This hydraulic stabilizer is particularly suitable for new line installations for deaerating of fiber stock suspensions whose design principles for the tank construction in each case is disclosed in the aforementioned U.S. Pat. No. 5,868,905 (PK10542 US).
A further embodiment of the invention provides that, the dwell duration of the preferably gas-free fiber stock suspension in the hydraulic stabilizer is between 2 and 80 seconds, preferably between 5 and 40 seconds; and the dwell volume of the preferably gas-free fiber stock suspension in the hydraulic stabilizer is between 0.8 and 100 m3, preferably between 4 and 70 m3. These parameters have the advantage that they ensure optimum design of the above constant section and optimum operation as far as runability, etc. of the paper or cardboard machine. The hydraulic stabilizer is located immediately or indirectly following the outlet opening for the preferably gas-free fiber stock suspension.
According to the preferred embodiment of the invention there is located between the outlet opening for the preferably gas-free fiber stock suspension and the hydraulic stabilizer, at least one tube or pipeline.
It is also understood that the aforementioned and subsequently further explained characteristics of the invention may be utilized not only in the cited combinations, but also in other combinations, or self-contained, without relinquishing the scope of the invention.
Additional characteristics and advantages of the invention result from the subclaims and the following description of preferred design examples, whereby reference is made to the drawings.